Anti-fuse with reduced programming voltage

ABSTRACT

A method for integrating transistors and anti-fuses on a device includes epitaxially growing a semiconductor layer on a substrate and masking a transistor region of the semiconductor layer. An oxide is formed on an anti-fuse region of the semiconductor layer. A semiconductor material is grown over the semiconductor layer to form an epitaxial semiconductor layer in the transistor region and a defective semiconductor layer in the anti-fuse region. Transistor devices in the transistor region and anti-fuse devices in the anti-fuse region are formed wherein the defective semiconductor layer is programmable by an applied field.

BACKGROUND Technical Field

The present invention generally relates to semiconductor devices andprocessing, and more particularly to anti-fuse structures integratedinto transistor device fabrication processes.

Description of the Related Art

Anti-fuses are commonly employed in the semiconductor industry.Anti-fuses are activated to create a connection between two or moreconductors. In one example, anti-fuses may be employed for one-timeprogramming purposes. The anti-fuse can be used to repair DRAM arrays byswapping defective cells with redundant cells and can also be used inproduct configuration, for updating and repairing devices.

Anti-fuses often require special processing for integration on chips.With supply and threshold voltages scaling down and device dimensionsshrinking, this becomes increasingly challenging.

SUMMARY

In accordance with an embodiment of the present principles, a method forintegrating transistors and anti-fuses on a device includes epitaxiallygrowing a semiconductor layer on a substrate and masking a transistorregion of the semiconductor layer. An oxide is formed on an anti-fuseregion of the semiconductor layer. A semiconductor material is grownover the semiconductor layer to form an epitaxial semiconductor layer inthe transistor region and a defective semiconductor layer in theanti-fuse region. Transistor devices in the transistor region andanti-fuse devices in the anti-fuse region are formed wherein thedefective semiconductor layer is programmable by an applied field.

Another method for integrating transistors and anti-fuses on a deviceincludes epitaxially growing a semiconductor layer on a substrate,masking a transistor region of the semiconductor layer with a paddielectric layer and forming an oxide on an anti-fuse region of thesemiconductor layer. The pad dielectric layer is removed, and asemiconductor material is grown over the semiconductor layer to form astrained semiconductor layer in the transistor region and a defectivesemiconductor layer in the anti-fuse region. Transistor devices in thetransistor region and anti-fuse devices in the anti-fuse region areformed by forming gate structures concurrently in the transistor regionand the anti-fuse region and forming source and drain regions adjacentto the gate structures in the transistor region and the anti-fuseregion, wherein the defective semiconductor layer in the anti-fuseregion is programmable by an applied field.

A semiconductor device having transistors and anti-fuses integratedthereon includes an epitaxially grown semiconductor layer formed on asubstrate. A transistor region includes a semiconductor material formedover the semiconductor layer to form a device channel for a transistor.An anti-fuse region includes a defective semiconductor layer formed onan oxide in the anti-fuse region. Gate structures are formed betweensource and drain regions in the transistor region and the anti-fuseregion, wherein the defective semiconductor layer is programmable by anapplied field on the gate structures in the anti-fuse region.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view showing a device having a paddielectric layer formed in a transistor region and an oxide grown in ananti-fuse region in accordance with the present principles;

FIG. 2 is a cross-sectional view showing the device of FIG. 1 having thepad dielectric layer removed, a semiconductor material formed as acrystalline semiconductor layer in the transistor region and a defectivesemiconductor layer formed in the anti-fuse region in accordance withthe present principles;

FIG. 3 is a cross-sectional view showing the device of FIG. 2 showinggate structures concurrently formed in the transistor region and theanti-fuse region in accordance with the present principles;

FIG. 4 is a cross-sectional view showing the device of FIG. 3 withcontacts concurrently formed in the transistor region and the anti-fuseregion in accordance with the present principles; and

FIG. 5 is a block/flow diagram showing methods for co-integratingtransistors and anti-fuses on a same chip in accordance with the presentprinciples.

DETAILED DESCRIPTION

In accordance with the present principles, devices and methods areprovided to integrate transistors (e.g., field effect transistors(FETs)) with anti-fuses on a same chip. In one embodiment, theanti-fuses are formed on a defective semiconductor layer while thetransistors are formed on a defect-free strained semiconductor layer.Defects in the defective semiconductor layer reduce dielectric breakdownvoltage. In this way, a defective semiconductor channel formed with thedefective semiconductor layer reduces the programming voltages needed toprogram the anti-fuse. The anti-fuses are preferably provided with a lowprogramming voltage that employs gate activation to program theanti-fuses.

An anti-fuse is an electrical device that performs the opposite functionto a fuse. A fuse breaks an electrically conductive path, and ananti-fuse creates an electrically conductive path. Anti-fuses may beemployed to permanently program integrated circuits (ICs). Certainprogrammable logic devices (PLDs), such as structured applicationspecific ICs (ASICs), use anti-fuse technology to configure logiccircuits and create a customized design from a standard IC design.Anti-fuse PLDs are usually a one-time programmable device that does notneed to be configured each time power is applied.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1−x) where x is less than or equal to 1, etc. Inaddition, other elements may be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein may be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers may also be present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a device 10 includes asubstrate 12 for integrating transistor devices and anti-fuses inaccordance with the present principles. The substrate 12 may include abulk semiconductor, a semiconductor-on-insulator (SOI), an extremelythin SOI (ETSOI), partially depleted SOI (PDSOI), or any other suitablesubstrate.

In one embodiment, a SOI substrate 12 may be employed having asemiconducting material 18 including, but not limited to Si, strainedSi, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, and InP, orany combination thereof. The semiconducting material 18 may be thinnedto a desired thickness by planarization, grinding, wet etch, dry etch,oxidation followed by oxide etch, or any combination thereof to createan ETSOI. One method of thinning the semiconducting material 18 is tooxidize by a thermal dry or wet oxidation process, and then wet etch theoxide layer using a hydrofluoric acid mixture. This process can berepeated to achieve the desired thickness. A base substrate 14 mayinclude a semiconducting material including, but not limited to Si,strained Si, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, InPas well as other III/V and II/VI compound semiconductors. A burieddielectric layer 16 may be disposed between the base 14 and thesemiconducting material 18. The buried dielectric layer 16 may include asilicon oxide or other suitable dielectric material.

An epitaxial layer 20 is grown on the semiconductor material 18. In oneembodiment, the epitaxial layer 20 may include SiGe if the semiconductorlayer 18 includes Si.

Epitaxial growth can be performed by ultrahigh vacuum chemical vapordeposition (UHVCVD), rapid thermal chemical vapor deposition (RTCVD),metalorganic chemical vapor deposition (MOCVD), low-pressure chemicalvapor deposition (LPCVD), limited reaction processing CVD (LRPCVD),molecular beam epitaxy (MBE), etc. Epitaxial materials may be grown fromgaseous or liquid precursors. Epitaxial materials may be grown usingvapor-phase epitaxy (VPE), molecular-beam epitaxy (MBE), liquid-phaseepitaxy (LPE), or other suitable process. Epitaxial silicon, silicongermanium (SiGe), and/or carbon doped silicon (Si:C) silicon can bedoped during deposition (in-situ doped) by adding dopants, n-typedopants (e.g., phosphorus or arsenic) or p-type dopants (e.g., boron orgallium), depending on the type of transistor. When SiGe is epitaxiallygrown, the SiGe may have germanium content in the range of 5% to 80%, orpreferably between 20% and 60%.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown,” mean the growth of a semiconductor material (crystallinematerial) on a deposition surface of another semiconductor material(crystalline material), in which the semiconductor material being grown(crystalline over layer) has substantially the same crystallinecharacteristics as the semiconductor material of the deposition surface(seed material). In an epitaxial deposition process, the chemicalreactants provided by the source gases are controlled, and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to moveabout on the surface such that the depositing atoms orient themselves tothe crystal arrangement of the atoms of the deposition surface.Therefore, an epitaxially grown semiconductor material has substantiallythe same crystalline characteristics as the deposition surface on whichthe epitaxially grown material is formed. For example, an epitaxiallygrown semiconductor material deposited on a {100} orientated crystallinesurface will take on a {100} orientation. In some embodiments, epitaxialgrowth and/or deposition processes are selective to forming onsemiconductor surface, and generally do not deposit material on exposedsurfaces, such as silicon dioxide or silicon nitride surfaces.

A pad dielectric layer 22 is deposited by, e.g., a chemical vapordeposition (CVD) and is patterned using lithography or other patterningprocess. The pad dielectric layer 22 may include a dielectric materialsuch as, e.g., a silicon nitride or other suitable material. Thepatterning of the pad dielectric layer 22 defines a region 60 wheretransistors will be formed and a region 62 where anti-fuses will beformed. The pad dielectric layer 22 acts as a hardmask to cover theregion 60 for FET devices.

In accordance with the pad dielectric layer 22, the epitaxially grownlayer 20 is modified. In one embodiment, the modification includes anoxidation of the layer 20. For example, if layer 20 includes SiGe a thinoxide layer 24 is formed on an exposed SiGe region (62) of layer 20.

Referring to FIG. 2, the pad dielectric layer 22 is stripped off thelayer 20. The strip may include a selective wet or dry etch. Anepitaxial growth process is performed over the device 10. In region 60,the epitaxial growth process results in the formation of amonocrystalline (defect free) layer 25, while in the region 62, theepitaxial process grows a defective semiconductor layer 26 due to theoxide layer 24. In one embodiment, the layer 25 includes Si in region60, and the Si may be strained if the underlying layer 24 is, e.g.,SiGe. In region 62, the defective semiconductor layer 26 may includedefective Si. In this way, strained Si 25 is formed in actual deviceregion 60, while defective Si 26 is formed in the anti-fuse deviceregion 62.

Defects in the anti-fuse device region 62 include dislocations, stackingfaults, grain boundaries, etc. Defect density ranges from 1×10⁶ to1×10¹²/cm². The defective layer can be doped or undoped. The thicknessof the defective layer 26 may be substantially the same, thicker, orthinner than the strained Si 25. The thickness of the defective layer 26may range from about 3 nm to about 20 nm, and more preferably betweenabout 5 to about 10 nm. The defects in the defective layer 26 willreduce the breakdown voltage of the gate dielectric in the anti-fusedevices.

Referring to FIG. 3, shallow trench isolation (STI) regions 40 areformed between regions and/or devices. The STI regions are formed byetching a trench into the semiconductor material 18 (or substrate)utilizing a conventional dry etching process such as reactive-ionetching (RIE) or plasma etching. The trenches may optionally be linedwith a conventional liner material, e.g., an oxide, and then CVD oranother like deposition process is employed to fill the trench withpolysilicon or another like STI dielectric material (oxide). The STIdielectric may optionally be densified after deposition. A conventionalplanarization process such as chemical-mechanical polishing (CMP) mayoptionally be used to provide a planar structure.

Gate structures 28, 30 are respectively formed in regions 60 and 62. Thegate structures 28, 30 are respectively formed directly on the strainedsemiconductor layer 25 and the defective semiconductor 26, in accordancewith one embodiment. The gate structures 28, 30 can be formed usingdeposition, photolithography and a selective etching process.Specifically, a pattern is produced by applying a photoresist to thesurface to be etched. The photoresist is exposed to a pattern ofradiation; and then the pattern is developed into the photoresistutilizing a resist developer. Once the patterning of the photoresist iscompleted, sections covered by the photoresist are protected while theexposed regions are removed using a selective etching process thatremoves the unprotected regions. In one embodiment, a hard mask(hereafter referred to as a dielectric cap 38) may be employed to formthe gate structures 28, 30. The dielectric cap 38 may be formed by firstdepositing a dielectric hard mask material, like SiN or SiO₂, atop alayer of gate electrode material (or gate conductor) 34 and thenapplying a photoresist pattern to the hard mask material using alithography process steps. The photoresist pattern is then transferredinto the hard mask material using a dry etch process forming thedielectric cap 38.

Next, the photoresist pattern is removed and the dielectric cap 38pattern is then transferred into the gate electrode material 34 during aselective etching process. The gate structures 28, 30 may include atleast a gate conductor 34 atop a gate dielectric 32. Gate conductor 34may be a metal gate electrode. The metal gate electrode 34 may be anyconductive metal including, but not limited to W, Ni, Ti, Mo, Ta, Cu,Pt, Ag, Au, Ru, Ir, Rh, and Re, and alloys that include at least one ofthese conductive elemental metals. The gate structures 28, 30 mayfurther include additional conductive material as the metal gateelectrode 34 or as part of the gate electrode 34. In one example, asecond conductive material may be a doped semiconductor material, suchas a doped silicon containing material, e.g., doped polysilicon. When acombination of conductive elements is employed, an optional diffusionbarrier material such as TaN or WN may be formed between the conductivematerials.

The gate conductor 34 of the gate structures is formed over the gatedielectric 32. The gate dielectric 32 may be a dielectric material, suchas SiO₂, or alternatively high-k dielectrics, such as oxides of Ta, Zr,Al, Hf or combinations thereof. The gate dielectric 32 may include,e.g., SiO₂, ZrO₂, Ta₂O₅ and/or Al₂O₃.

Dielectric spacers 36 are formed over the gates structures 28, 30 onsidewalls thereof. The dielectric spacers 36 may be formed by using aconformal blanket layer deposition, such as chemical vapor deposition,and an anisotropic etch back. The dielectric spacers 36 may be composedof a dielectric, such as a nitride, oxide, oxynitride, or a combinationthereof.

It should be understood that the gate structures 28, 30 may be formed asreal gates, as in the case of a gate-first method or may be formed as adummy gate in the case of gate-last method. A replacement metal gate(RMG) FinFET can be fabricated on strained Si 25 in region 60 and on thedefective Si 26 in region 62.

Referring to FIG. 4, source and drain regions 42, 44 are formed on thelayers 25 and 26 respectively. A number of different sources may be usedfor the deposition of the semiconductor material that forms raisedsource/drain regions 42, 44. In some embodiments, in which thesemiconductor material that forms the raised source/drain regions 42, 44is composed of silicon, the silicon gas source for epitaxial depositionmay be selected from the group consisting of hexachlorodisilane(Si₂Cl₆), tetrachlorosilane (SiCl₄), dichlorosilane (Cl₂SiH₂),trichlorosilane (Cl₃SiH), methylsilane ((CH₃)SiH₃), dimethylsilane((CH₃)₂SiH₂), ethylsilane ((CH₃CH₂)SiH₃), methyldisilane ((CH₃)Si₂H₅),dimethyldisilane ((CH₃)₂Si₂H₄), hexamethyldisilane ((CH₃)₆Si₂) andcombinations thereof. In some embodiments, in which the semiconductormaterial that forms the raised source/drain regions 42, 44 is composedof germanium, the germanium gas source for epitaxial deposition may beselected from the group consisting of germane (GeH₄), digermane (Ge₂H₆),halogermane, dichlorogermane, trichlorogermane, tetrachlorogermane andcombinations thereof. In some embodiments, in which the semiconductormaterial that forms the raised source/drain region 42, 44 is composed ofsilicon germanium, the silicon sources for epitaxial deposition may beselected from the group consisting of silane, disilane, trisilane,tetrasilane, hexachlorodisilane, tetrachlorosilane, dichlorosilane,trichlorosilane, methylsilane, dimethylsilane, ethylsilane,methyldisilane, dimethyldisilane, hexamethyldisilane and combinationsthereof, and the germanium gas sources may be selected from the groupconsisting of germane, digermane, halogermane, dichlorogermane,trichlorogermane, tetrachlorogermane and combinations thereof.

The raised source/drain regions 43, 45 may be formed during the sameepitaxial growth method but may include defects from the underlyinglayer 26. The raised source/drain regions 42, 43, 44, 45 may be formedusing a selective deposition process (e.g., epitaxy for semiconductormaterial) and are therefore self-aligned using the STIs 40 and gatestructures 28, 30.

Following the formation of source/drain regions, a layer of dielectricmaterial 48 is blanket deposited atop the entire substrate andplanarized. The blanket dielectric may be selected from the groupconsisting of silicon-containing materials such as SiO₂, Si₃N₄,SiO_(x)N_(y), SiC, SiCO, SiCOH, and SiCH compounds; the above-mentionedsilicon-containing materials with some or all of the Si replaced by Ge;carbon-doped oxides; inorganic oxides; inorganic polymers; hybridpolymers; organic polymers such as polyamides or SiLK™; othercarbon-containing materials; organo-inorganic materials such as spin-onglasses and silsesquioxane-based materials; and diamond-like carbon(DLC, also known as amorphous hydrogenated carbon, a-C:H). Additionalchoices for the blanket dielectric 48 may include: any of theaforementioned materials in porous form, or in a form that changesduring processing to or from being porous and/or permeable to beingnon-porous and/or non-permeable.

The blanket dielectric 48 may be formed by various methods well known tothose skilled in the art, including, but not limited to: spinning fromsolution, spraying from solution, chemical vapor deposition (CVD),plasma enhanced CVD (PECVD), sputter deposition, reactive sputterdeposition, ion-beam deposition and evaporation.

The deposited dielectric 48 is then patterned and etched to forth viaholes to the various source/drain and gate conductor regions of thedevice 10. Following via formation, interconnects or contacts 46 areformed by depositing a conductive metal into the via holes using, e.g.,CVD. The contacts 46 may include any suitable conductive material, suchas polycrystalline or amorphous silicon, germanium, silicon germanium, ametal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt,copper, aluminum, lead, platinum, tin, silver, gold), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tungsten silicide, tungsten nitride, ruthenium oxide, cobalt silicide,nickel silicide), carbon nanotube, conductive carbon, graphene, or anysuitable combination of these materials. The conductive material mayfurther comprise dopants that are incorporated during or afterdeposition.

In accordance with the present principles, FETs 50 are formed on a samedevice as anti-fuses 52. The anti-fuses 52 include defective Si (orother materials) and can be turned on to make a connection between thesource/drain regions 43, 45 through the defective layer 26. In oneembodiment, the anti-fuse 52 is programmed using a field effect of thegate 30. When the gate is activated, the defective layer 26 is alteredto provide a conductive path (short) between the source/drain regions43, 45. In one embodiment, the defective layer 26 is configured to makea permanent conductive path. The permanent path is programmed afterfabrication is complete using only the voltages available on-chip. Forexample, a supply voltage or threshold voltage for the FETs 50 may beemployed to permanently program the anti-fuse 52. The threshold voltageis considered a low voltage for programming the fuse, and may be betweenabout +/−0.5 volts to about +/−3 volts for a 2 nm gate dielectric.

The anti-fuse 52 works as follows. An electrical field across the gatedielectric 32 can break the gate dielectric when the electric fieldexceeds the breakdown electric field of the gate dielectric 32. Oncebreakdown occurs, the gate current increases significantly. If the gatedielectric 32 is not broken, the gate current is much smaller. Toprogram an anti-fuse, the source and drain are grounded and a largevoltage is applied to the gate 30, creating a large electric fieldacross the gate dielectric 32 to break down the gate dielectric 32.Current can flow from the gate 30 to the defective silicon channel 26and the source/drain 43/45. For example, the gate dielectric may includehafnium oxide with a thickness of 2 nm, a gate voltage of 3 volts canbreak down the gate dielectric in this case.

Referring to FIG. 5, methods for integrating transistors and anti-fuseson a same device are provided in accordance with illustrativeembodiments. In some alternative implementations, the functions noted inthe blocks may occur out of the order noted in the figures. For example,two blocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts or carry outcombinations of special purpose hardware and computer instructions.

In block 102, a semiconductor layer is epitaxially grown on a substrate.The substrate may take any form, e.g., ETSOI, SOI, bulk, etc. In block104, a transistor region of the semiconductor layer is masked with a paddielectric layer. The pad dielectric layer is patterned, e.g., usinglithography or other process, to protect the transistor region fromoxidation during subsequent processing. In block 106, an oxide (or othercompound) is formed on an anti-fuse region of the semiconductor layer.While an oxide is preferred, other chemical reactions may be employed tocreate a defective semiconductor in subsequent steps. The oxide may begrown by exposing the semiconductor layer to oxygen-containing speciesin accordance with the pad dielectric. In block 108, the pad dielectriclayer is removed, e.g., by selective etching.

In block 110, a semiconductor material is grown over the semiconductorlayer to form a semiconductor layer, which may be strained, in thetransistor region and a defective semiconductor layer in the anti-fuseregion. The semiconductor material is grown using an epitaxial growthprocess. In block 112, transistor devices are formed in the transistorregion and anti-fuse devices are formed in the anti-fuse region. Inblock 114, gate structures are concurrently formed in the transistorregion and the anti-fuse region. The gate structures may include a gatedielectric, a gate conductor, a gate cap and spacers.

In block 116, source and drain regions are formed adjacent to the gatestructures in the transistor region and the anti-fuse region. The sourceand drain regions may be epitaxially grown on the semiconductor material(e.g., strain semiconductor in the transistor region and defectivesemiconductor in the anti-fuse region). In one embodiment, thesemiconductor layer includes SiGe and the semiconductor materialincludes strained Si in the transistor region and defective Si in theanti-fuse region. The defective semiconductor layer in the anti-fuseregion is programmable by an applied field.

In block 118, shallow trench isolation (STI) regions are formed. The STIregions may be formed between the transistor region and the anti-fuseregion. In block 120, an interlevel dielectric layer is formed,planarized and patterned. Contacts are concurrently formed in thetransistor region and the anti-fuse region by depositing conductivematerial followed by a planarization process (e.g., CMP). In block 122,anti-fuses are programmed in the anti-fuse region by activating a gateof the gate structure in the anti-fuse region. This is performed afterthe device is completed. The anti-fuse may be employed to activate aredundant array or to short circuit a component(s) on the device.

Having described preferred embodiments for an anti-fuse with reducedprogramming voltage (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A semiconductor device having transistors andanti-fuses integrated thereon, comprising: a substrate; a transistorregion having a defect free monocrystalline semiconductor layer and adevice channel for a transistor; an anti-fuse region including adefective semiconductor layer formed on an oxide of a portion of thesurface of an epitaxial semiconductor layer over which the transistor isformed, a surface of the oxide nearest to the substrate being closer tothe substrate than a surface of the defect free monocrystallinesemiconductor layer nearest to the substrate; and gate structures formedin the transistor region and in the anti-fuse region, wherein thedefective semiconductor layer is programmable by an applied field on thegate structures in the anti-fuse region.
 2. The device as recited inclaim 1, further comprising contacts formed in the transistor region andthe anti-fuse region.
 3. The device as recited in claim 1, wherein thedefective semiconductor layer includes Si and forms a conductive path byactivating a gate of the gate structure in the anti-fuse region above athreshold voltage.
 4. The device as recited in claim 1, wherein thesemiconductor layer includes SiGe and a semiconductor material includesstrained Si in the transistor region.
 5. The device as recited in claim1, further comprising: a shallow trench isolation region formed betweenthe transistor region and the anti-fuse region.
 6. The device as recitedin claim 1, wherein the source and drain regions are formed on thesemiconductor material in the transistor region and the defectivesemiconductor layer in the anti-fuse region.
 7. The device as recited inclaim 1, wherein the defective semiconductor layer's defects include atleast one of dislocations, stacking faults, and grain boundaries.
 8. Thedevice as recite in claim 1, wherein a semiconductor material in thetransistor region and the defective semiconductor layer are eachconcurrently formed from a common epitaxially grown layer.
 9. The deviceas recited in claim 1, wherein a thickness of the defectivesemiconductor layer is between about 3 nanometers and about 20nanometers.
 10. The device as recited in claim 1, further includingsource and drain regions in the anti-fuse region including defects fromthe defective semiconductor layer.
 11. The device as recited in claim 1,wherein a defect density of the defective semiconductor layer is betweenabout 1×10⁶/cm² and about 1×10¹²/cm².
 12. A semiconductor device havingtransistors and anti-fuses integrated thereon, comprising: a substrate;a transistor region including a defect free monocrystalline strainedsemiconductor material formed over a semiconductor layer to form adevice channel for a transistor; an anti-fuse region including: anoxidized surface of the semiconductor layer in the anti-fuse regionforming an oxide layer, a surface of the oxide layer nearest to thesubstrate being closer to the substrate than a surface of the defectfree monocrystalline strained semiconductor material nearest to thesubstrate; a defective semiconductor layer epitaxially grown on theoxidized surface in the anti-fuse region; and gate structures formed inthe transistor region and in the anti-fuse region, wherein the defectivesemiconductor layer is programmable by an applied field on the gatestructures in the anti-fuse region.
 13. The device as recited in claim12, wherein the strained semiconductor material in the transistor regionand the defective semiconductor layer are each concurrently formed froma common epitaxially grown layer.
 14. The device as recited in claim 12,wherein a thickness of the defective semiconductor layer is betweenabout 3 nanometers and about 20 nanometers.
 15. The device as recited inclaim 12, wherein the defective semiconductor layer includes Si andforms a conductive path by activating a gate of the gate structure inthe anti-fuse region above a threshold voltage.
 16. The device asrecited in claim 12, wherein the semiconductor layer includes SiGe andthe strained semiconductor material includes strained Si in thetransistor region.
 17. The device as recited in claim 12, furthercomprising: a shallow trench isolation region formed between thetransistor region and the anti-fuse region.
 18. The device as recited inclaim 12, further including source and drain regions are formed on thestrained semiconductor material in the transistor region and on thedefective semiconductor layer in the anti-fuse region.
 19. The device asrecited in claim 12, further including source and drain regions in theanti-fuse region including defects from the epitaxially grownsemiconductor layer.
 20. The device as recited in claim 12, wherein adefect density of the defective semiconductor layer is between about1×10⁶/cm² and about 1×10¹²/cm².